Dirt Bike Engine
Dirt Bike Engine Parts at JJ Motorsports
Discover a full range of dirt bike engine components for rebuilding or upgrading your performance from JJ Motorsports. From crankshafts to cylinder heads and piston kits, these precision-engineered components ensure reliable performance. For additional upgrades, check out our full selection of off-road dirt bike parts to keep your engine running at peak efficiency on the track or trails.
Shop trusted brands like Wiseco for forged piston kits and K&N for high-flow oil filters. Explore related categories such as Dirt Bike Air and Fuel for intake upgrades or Dirt Bike Exhaust for complete systems.
Browse our in-stock inventory below with same-day shipping and expert support. Questions? Contact us for fitment advice!
- Product
- Qty in Cart
- Quantity
- Price
- Subtotal
-
PROX Valve Shim - 5 pack 29.948240
PROX
$10.95Valve shim clearance is critical to engine performance and longevity—even slight deviations compromise timing and increase wear on critical components. PROX Valve Shims are precision-machined to exact tolerances and heat-treated for superior hardness,...09260966- SKU:
- 09260966
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- RIDING STYLE:
- OFF-ROAD
- RIDING STYLE:
- WATERCRAFT
- VALVE SHIM THICKNESS METRIC:
- 2.40 MM
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- SNOW
- RIDING STYLE:
- UTV
- TYPE:
- VALVE
- UNITS:
- 5 PACK
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- ATV
- OUTSIDE DIAMETER METRIC:
- 9.48 MM
- RIDING STYLE:
- STREET
$10.95 -
PROX Valve Shim - 5 pack 29.948245
PROX
$10.95Valve shimming is critical to maintaining proper valve clearance and preventing catastrophic engine damage from valve float or seat wear. These PROX shims are precision-machined to exact tolerances and heat-treated for superior hardness, ensuring...09260967- SKU:
- 09260967
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- RIDING STYLE:
- OFF-ROAD
- RIDING STYLE:
- WATERCRAFT
- OUTSIDE DIAMETER METRIC:
- 9.48 MM
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- ATV
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- SNOW
- RIDING STYLE:
- UTV
- TYPE:
- VALVE
- UNITS:
- 5 PACK
- RIDING STYLE:
- STREET
- VALVE SHIM THICKNESS METRIC:
- 2.45 MM
$10.95 -
PROX Valve Shim - 5 pack 29.948250
PROX
$10.95Valve shims are critical wear items in high-performance engines, and precision tolerances directly impact valve timing, lift, and overall engine reliability. The PROX Valve Shim 5-pack ensures consistent performance across multiple shim changes without...09260968- SKU:
- 09260968
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- RIDING STYLE:
- ATV
- RIDING STYLE:
- OFF-ROAD
- TYPE:
- VALVE
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- SNOW
- RIDING STYLE:
- UTV
- RIDING STYLE:
- WATERCRAFT
- UNITS:
- 5 PACK
- OUTSIDE DIAMETER METRIC:
- 9.48 MM
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- VALVE SHIM THICKNESS METRIC:
- 2.50 MM
- RIDING STYLE:
- STREET
$10.95 -
PROX Valve Shim - 5 pack 29.948265
PROX
$10.95Valve timing precision directly impacts your engine's power delivery and reliability—even micron-level inconsistencies compound into performance loss and premature wear. PROX valve shims are heat-treated to withstand extreme combustion pressures and...09260971- SKU:
- 09260971
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- OUTSIDE DIAMETER METRIC:
- 9.48 MM
- RIDING STYLE:
- STREET
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- ATV
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- OFF-ROAD
- RIDING STYLE:
- SNOW
- RIDING STYLE:
- UTV
- TYPE:
- VALVE
- UNITS:
- 5 PACK
- RIDING STYLE:
- WATERCRAFT
- VALVE SHIM THICKNESS METRIC:
- 2.65 MM
$10.95 -
PROX Valve Shim - 5 pack 29.948275
PROX
$10.95Valve shim clearance is critical to engine reliability and performance—get it wrong, and you're risking bent valves, poor sealing, and costly damage. PROX Valve Shims are precision-machined to exact tolerances and heat-treated for superior hardness,...09260973- SKU:
- 09260973
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- OUTSIDE DIAMETER METRIC:
- 9.48 MM
- RIDING STYLE:
- ATV
- RIDING STYLE:
- STREET
- RIDING STYLE:
- OFF-ROAD
- TYPE:
- VALVE
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- SNOW
- RIDING STYLE:
- UTV
- RIDING STYLE:
- WATERCRAFT
- UNITS:
- 5 PACK
- VALVE SHIM THICKNESS METRIC:
- 2.75 MM
$10.95 -
PROX Valve Shim - 5 pack 29.948285
PROX
$10.95Valve shim selection directly impacts your engine's valve clearance, combustion efficiency, and component longevity. The PROX Valve Shim 5-pack delivers precision-engineered shims with heat-treated hardness to minimize wear and maintain tight tolerances...09260975- SKU:
- 09260975
- Availability:
- Ships Same Business Day
- Weight:
- 0.05 LBS
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- SNOW
- RIDING STYLE:
- WATERCRAFT
- UNITS:
- 5 PACK
- RIDING STYLE:
- OFF-ROAD
- RIDING STYLE:
- UTV
- TYPE:
- VALVE
- RIDING STYLE:
- ATV
- RIDING STYLE:
- STREET
- VALVE SHIM THICKNESS METRIC:
- 2.85 MM
- OUTSIDE DIAMETER METRIC:
- 9.48 MM
$10.95 -
PROX Valve Shim - 5 pack 29.948290
PROX
$10.95Valve shim clearance directly impacts engine performance, combustion efficiency, and component longevity. PROX Valve Shims are precision-machined to exact tolerances, eliminating guesswork during valve adjustment and ensuring consistent performance...09260976- SKU:
- 09260976
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- SNOW
- RIDING STYLE:
- UTV
- UNITS:
- 5 PACK
- RIDING STYLE:
- STREET
- RIDING STYLE:
- WATERCRAFT
- RIDING STYLE:
- OFF-ROAD
- VALVE SHIM THICKNESS METRIC:
- 2.90 MM
- OUTSIDE DIAMETER METRIC:
- 9.48 MM
- RIDING STYLE:
- ATV
- TYPE:
- VALVE
$10.95 -
PROX Valve Shim Kit 29.VSA1000
PROX
$99.95Valve shims are critical wear items that directly impact valve clearance, combustion efficiency, and engine longevity. OEM replacements come with premium pricing and extended lead times—the PROX Valve Shim Kit 29.VSA1000 delivers precision-matched...09260989- SKU:
- 09260989
- Availability:
- Ships Same Business Day
- Weight:
- 0.67 LBS
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- RIDING STYLE:
- STREET
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- SNOW
- RIDING STYLE:
- UTV
- TYPE:
- VALVE
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- ATV
- VALVE SHIM THICKNESS METRIC:
- 1.85 MM - 3.20 MM
- RIDING STYLE:
- OFF-ROAD
- RIDING STYLE:
- WATERCRAFT
- UNITS:
- KIT
$99.95 -
PROX Valveshim - 10.00 x 2.20 - 5 pack 29.100220
PROX
$9.95Valve shims are critical wear components that directly impact your engine's valvetrain precision and longevity. OEM replacements are expensive and require frequent servicing—PROX valveshims deliver OEM-equivalent performance at a fraction of the cost,...09260997- SKU:
- 09260997
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- RIDING STYLE:
- OFF-ROAD
- TYPE:
- VALVE
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- VALVE SHIM THICKNESS METRIC:
- 2.20 MM
- PRODUCT NAME:
- SHIM KIT
- UNITS:
- 5 PACK
$9.95 -
PROX Valveshim - 10.00 x 2.45 - 5 pack 29.100245
PROX
$9.95Valve shims are critical wear items that directly impact your engine's valve clearance, combustion efficiency, and overall reliability. The PROX 10.00 x 2.45 shim delivers precision-engineered durability at a fraction of OEM replacement costs, making it...09261002- SKU:
- 09261002
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- RIDING STYLE:
- OFF-ROAD
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- TYPE:
- VALVE
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- UNITS:
- 5 PACK
- VALVE SHIM THICKNESS METRIC:
- 2.45 MM
$9.95 -
PROX Valveshim - 10.00 x 2.50 - 5 pack 29.100250
PROX
$10.95Valve shim adjustment is critical to proper engine tuning, and worn or incorrect shims compromise performance and longevity. The PROX Valveshim 10.00 x 2.50 offers a precision-engineered alternative to expensive OEM replacements, delivering reliable...09261003- SKU:
- 09261003
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
- TYPE:
- VALVE
- RIDING STYLE:
- OFF-ROAD
- PRODUCT NAME:
- SHIM KIT
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- UNITS:
- 5 PACK
- VALVE SHIM THICKNESS METRIC:
- 2.50 MM
$10.95 -
PROX Valveshim - 10.00 x 2.55 - 5 pack 29.100255
PROX
$10.95Valve shims are critical to maintaining proper valve clearance and engine performance, and worn or damaged shims can lead to costly compression loss and improper valve timing. The PROX Valveshim 10.00 x 2.55 delivers OEM-equivalent precision at a...09261004- SKU:
- 09261004
- Availability:
- Ships Same Business Day
- Weight:
- 0.02 LBS
- RIDING STYLE:
- OFF-ROAD
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- RIDING STYLE:
- STREET
- PRODUCT NAME:
- SHIM KIT
- TYPE:
- VALVE
- UNITS:
- 5 PACK
- VALVE SHIM THICKNESS METRIC:
- 2.55 MM
- OUTSIDE DIAMETER METRIC:
- 10.00 MM
$10.95 -
PROX Piston Kit 01.1338.A
PROX
$188.95A worn or damaged piston compromises compression, throttle response, and fuel efficiency—ultimately costing you performance and reliability. The PROX Piston Kit 01.1338.A restores your engine to OEM specifications with Japanese-manufactured precision,...09101126- SKU:
- 09101126
- Availability:
- Ships Same Business Day
- Weight:
- 0.50 LBS
- BORE SIZE METRIC:
- 77.97 MM
- ENGINE TYPE:
- 4-STROKE
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PISTON SIZE METRIC:
- STANDARD
- PRODUCT NAME:
- PISTON KIT
- UNITS:
- EACH
- PISTON DIAMETER METRIC:
- 77.97 MM
- RIDING STYLE:
- OFF-ROAD
$188.95 -
PROX Piston Kit 01.1338.C
PROX
$188.95When your engine's internals are worn or damaged, OEM-equivalent pistons are non-negotiable for reliable performance and longevity. The PROX Piston Kit 01.1338.C delivers factory-quality construction with Japanese precision manufacturing, ensuring your...09101128- SKU:
- 09101128
- Availability:
- Ships Same Business Day
- Weight:
- 0.51 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- ENGINE TYPE:
- 4-STROKE
- BORE SIZE METRIC:
- 77.99 MM
- RIDING STYLE:
- OFF-ROAD
- PISTON DIAMETER METRIC:
- 77.99 MM
- PISTON SIZE METRIC:
- STANDARD
- PRODUCT NAME:
- PISTON KIT
$188.95 -
PROX Piston Kit 01.1339.B
PROX
$185.95When your engine's pistons show wear or you're rebuilding after a high-mileage season, settling for substandard replacements risks catastrophic failure and lost performance. The PROX Piston Kit 01.1339.B delivers OEM-equivalent reliability with precision...09101130- SKU:
- 09101130
- Availability:
- Ships Same Business Day
- Weight:
- 0.50 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- ENGINE TYPE:
- 4-STROKE
- PISTON DIAMETER METRIC:
- 77.98 MM
- PISTON SIZE METRIC:
- STANDARD SIZE B
- UNITS:
- EACH
- RIDING STYLE:
- OFF-ROAD
- BORE SIZE METRIC:
- 77.98 MM
- PRODUCT NAME:
- PISTON KIT
$185.95 -
PROX Piston Kit 01.2406.C
PROX
$179.95When your engine demands reliability and precision, OEM-quality pistons are non-negotiable. The PROX Piston Kit 01.2406.C delivers Japanese manufacturing standards with CNC-machined tolerances that restore your engine's original performance...09101133- SKU:
- 09101133
- Availability:
- Ships Same Business Day
- Weight:
- 0.57 LBS
- PISTON DIAMETER METRIC:
- 76.97 MM
- BORE SIZE METRIC:
- 76.97 MM
- RIDING STYLE:
- OFF-ROAD
- ENGINE TYPE:
- 4-STROKE
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE A
- PRODUCT NAME:
- PISTON KIT
$179.95 -
PROX Piston Kit 01.3338.A
PROX
$188.95A piston kit is the foundation of reliable engine performance—worn or inadequate pistons lead to compression loss, poor combustion, and premature engine failure. The PROX Piston Kit 01.3338.A delivers OEM-equivalent durability with precision...09101145- SKU:
- 09101145
- Availability:
- Ships Same Business Day
- Weight:
- 0.48 LBS
- PISTON MATERIAL:
- ALUMINUM ALLOY
- RIDING STYLE:
- OFF-ROAD
- UNITS:
- EACH
- BORE SIZE METRIC:
- 76.96 MM
- PISTON SIZE METRIC:
- STANDARD SIZE A
- PISTON DIAMETER METRIC:
- 76.96 MM
- PRODUCT NAME:
- PISTON KIT
$188.95 -
PROX Piston Kit 01.4337.B
PROX
$188.95When your engine demands precision and reliability, compromised pistons aren't an option. The PROX Piston Kit 01.4337.B delivers OEM-equivalent performance with the durability required for high-demand racing and rebuilt engine applications. Built from...09101154- SKU:
- 09101154
- Availability:
- Ships Same Business Day
- Weight:
- 0.55 LBS
- PISTON SIZE METRIC:
- STANDARD SIZE B
- PISTON MATERIAL:
- ALUMINUM ALLOY
- PRODUCT NAME:
- PISTON KIT
- RIDING STYLE:
- ADVENTURE TOURING / DUAL-SPORT
- UNITS:
- EACH
- BORE SIZE METRIC:
- 76.97 MM
- PISTON DIAMETER METRIC:
- 76.97 MM
$188.95 -
PROX Piston Kit 01.4337.C
PROX
$179.95When your engine demands reliability under extreme conditions, OEM-quality pistons aren't optional—they're essential. The PROX Piston Kit 01.4337.C delivers factory-spec performance with precision engineering, ensuring consistent compression, reduced...09101155- SKU:
- 09101155
- Availability:
- Ships Same Business Day
- Weight:
- 0.55 LBS
- PRODUCT NAME:
- PISTON KIT
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- BORE SIZE METRIC:
- 76.98 MM
- PISTON DIAMETER METRIC:
- 76.98 MM
- RIDING STYLE:
- OFF-ROAD
- PISTON SIZE METRIC:
- STANDARD SIZE C
$179.95 -
PROX Piston Kit 01.4406.C
PROX
$189.95When your engine is pushing limits, your pistons need to match that intensity. The PROX Piston Kit 01.4406.C delivers OEM-equivalent reliability with Japanese manufacturing precision, ensuring consistent performance across extended high-RPM sessions...09101158- SKU:
- 09101158
- Availability:
- Ships Same Business Day
- Weight:
- 0.92 LBS
- PISTON DIAMETER METRIC:
- 95.99 MM
- PISTON MATERIAL:
- ALUMINUM ALLOY
- UNITS:
- EACH
- PISTON SIZE METRIC:
- STANDARD SIZE C
- RIDING STYLE:
- OFF-ROAD
- BORE SIZE METRIC:
- 95.99 MM
- PRODUCT NAME:
- PISTON KIT
$189.95
